1. Field of the Invention
The present invention relates to a hybrid construction machine in which a power unit is formed by connecting three devices, that is, an engine, a generator motor, and a hydraulic pump in series with each other.
2. Description of the Related Art
As shown in FIG. 5, in an excavator, an upper rotating structure 2, disposed on a crawler-type lower traveling structure 1, is mounted so as to be rotatable around a vertical axis that is perpendicular to the ground, and a working attachment 3 is mounted to a front portion of the upper rotating structure 2.
A cabin 5, a counterweight 6, and an engine room 7 are provided at the upper rotating structure 2. The cabin 5 is provided at the left side of a front portion of an upper frame 4 serving as a base. The counterweight 6 is provided at a back end portion of the upper frame 4. The engine room 7 is provided at a back portion (forwardly of the counterweight 6) of the upper rotating structure 2. An engine 8 is set as a power source in a left-right direction in the engine room 7.
In the specification, “front/back” and “left/right” are defined as viewed from an operator sitting in the cabin 5.
FIG. 6 shows an arrangement of devices in an engine room 7 of a hydraulic excavator having only an engine 8 as a power source, as viewed from a back side of a machine.
In the hydraulic excavator, as in the illustration, a power unit U1 is formed by connecting a hydraulic pump 9 in series with the engine 8. Reference numeral 10 denotes a cooling fan directly connected to the engine 8.
In the power unit U1 of the hydraulic excavator, a center of gravity X1 of the entire unit when viewed from the back side (or a front side) is slightly displaced towards the pump from an engine center of gravity X2.
As a mounting structure that supports the power unit U1 on a body frame (upper frame 4) of the machine, mount devices 11 and 12 are provided on respective sides of the center of gravity X1 of the power unit in an axial direction.
More specifically, the mount device at one side (hereunder referred to as the “left mount device” in accordance with directions defined in FIG. 6) 11 is provided at the engine 8. The mount device at the other side (hereunder referred to as the “right mount device” in accordance with directions defined in FIG. 6) 12 is provided at a fly wheel housing 13 accommodating a fly wheel.
The mount devices 11 and 12 each include a vibration absorbing mechanism that attenuates vibration by a resilient member such as rubber or a spring.
In this mounting structure, the distance between the center of gravity X1 of the power unit and one of supporting points and the distance between the center of gravity X1 of the power unit and the other of the supporting points are substantially equal to each other. Accordingly, the overall weight of the power unit U1 is substantially equally shared by the mount devices 11 and 12 at both sides.
The power unit mounting structure in the hydraulic excavator is discussed in Japanese Unexamined Patent Application Publication No. 2003-90387 (Patent Document 1).
In a hybrid excavator using both motive power and electric power, as shown in FIG. 7, a power unit U2 is formed by providing a generator motor 14 between an engine 8 and a hydraulic pump 9. The generator motor 14 operates as an electric generator and an electric motor.
An engine-side flange 15 and a pump-side flange 16 are provided on the left and right of the generator motor 14, respectively, so as to project towards the outer periphery while they act as end covers.
The flanges 15 and 16 are formed of thick plates, respectively. The engine-side flange 15 is connected to a fly wheel housing 13 at the engine 8, and the pump-side flange 16 is connected to the hydraulic pump 9.
The entire structure of the hybrid excavator is discussed in Japanese Unexamined Patent Application Publication No. 2002-227241 (Patent Document 2).
In the power unit U2 of the hybrid excavator, as in the illustration, a center of gravity X3 of the power unit is shifted considerably towards the hydraulic pump 9 from the center of gravity X1 of the power unit U1 for the hydraulic excavator in accordance with the addition of the generator motor 14.
Therefore, if the mounting structure provided on the basis of the specification of the hydraulic excavator shown in FIG. 6 is used as it is in the hybrid excavator, the distance between the center of gravity X3 of the power unit and one of supporting points and the distance between the center of gravity X3 of the power unit and the other of the supporting points differ greatly. Therefore, the stability of a supporting state becomes extremely poor.
More specifically, since an unbalanced load acts, for example, the left mount device may have insufficient strength due to an increase in load on the left mount device 11, or vibration may tend to occur.
The generator motor 14 is not directly supported. Therefore, its own weight and the weight of the hydraulic pump act upon the generator motor 14. Consequently, a force is forcefully generated at an internal structure through a rotary shaft, thereby adversely affecting the durability and performance of the generator motor 14.